Always write new content or update old content but never republish your old already published and indexed content.

Google knows what you doing it can impacts you site SEO, so better you should write you new content if that not the case you should update you old content.

Depends upon few different factors i think!

How often is MOZ bot is coming on your site and how many time it had crawled it and moreover do you have any backlinks on that Page or Post.

All those factors i think collectively select when and how much they should update your site DA and PA.

Depends upon few different factors i think!

How often is MOZ bot is coming on your site and how many time it had crawled it and moreover do you have any backlinks on that Page or Post.

All those factors i think collectively select when and how much they should update your site DA and PA.

There are many tools available to check Domain Age.

You can Google like "Domain Age checker" and you will see dozen of results and here you go your work is done.

First of all we need to understand how Moz Increases our DA?

The Answer is How and from where you are getting backlinks.

If you are getting links from low DA sites it will increases your sites DA But on other side if you are getting links from High DA Sites then there is high chance that your DA will increases.

Moreover all of these links needs to be indexed also. If these Links are not indexed no matter how much Backlinks you had made they are good for site maybe but for increasing your DA no its not gonna work.

Best way to reduce Spam score is look at your Site Backlinks.

If they are coming from spammed sites it will spam your site.

I hope you understand.